1.1 Upper Die of Bending Machine
The upper die, also known as the bending blade, can be classified into two types: integral and segmented. The integral upper die has two lengths: 415mm and 835mm. The segmented upper die comes in lengths of 10, 15, 20, 40, 50, 100 (left ear), 100 (right ear), 200, and 300mm. By using segmented dies, different bending lengths can be achieved.
The upper die can be further classified into four types: straight, curved, arc, and special.
1.1.1 Straight Die Types and Processing Characteristics
Straight dies are suitable for bending symmetrical products and can be positioned in both the forward and backward directions. The die thickness is 6mm, allowing for a minimum bending opening of 6mm.
Die Analysis: From the die bending simulation diagram, it can be observed that the die can be positioned both forward and backward. However, the lengths of Z and W should be smaller than those of X and Y. The die tip angle is 88 degrees with a tip radius of 0.2. Additionally, dies with tip angles of 30 degrees and 45 degrees are commonly used.
Die Analysis: The die tip angle is 30 degrees with a tip radius of 0.67. This die can be used to bend angles from 30 to 180 degrees. The small angle at the die tip allows for avoiding punch holes or nuts. It can also be used for deep insertion applications, with the die being positionable both forward and backward.
1.1.2 Curved Die Types and Processing Characteristics
Die Analysis: The bending process mainly relies on the W-direction positioning. When X > 15mm, the positioning effect becomes worse, and when Y > 30, the bending conditions are met. Otherwise, the die will hit the die back. This type of die is commonly known as the small curved die.
Die Analysis: The bending process mainly relies on the W-direction positioning. When X > 25mm, the positioning effect becomes worse, and when Y > 75, the bending conditions are met. Otherwise, the die will hit the die back. This type of die is commonly known as the large curved die.
1.1.3 Arc Die Types and Processing Characteristics
Die Analysis: Arc dies can be divided into fixed and movable types. Arc dies are used by replacing the circular rod to meet different arc bending requirements. When the X dimension is greater than 10mm, the fixed arc die has the same positioning effect as the small curved die. The selection criterion for the lower die V-groove is generally the diameter of the arc plus two sheet thicknesses.
1.1.4 Special Die Types and Processing Characteristics
Special dies for bending machines include step difference dies, flattening dies, and special-shaped bending upper dies.
A: The existing step difference dies are available in two lengths: 415mm and 835mm. The segmented sizes correspond to the specifications of the segmented dies. The forming diagram shows the bending shapes. However, when the plate thickness is relatively thick, such as T=2.0, it becomes difficult to form considering the severe indentation and limitations of the die.
B: The flattening die consists of a flat upper die, and a regular bending lower die can be used as a substitute, avoiding the V-groove. It is mainly used for edge flattening, pressing rivet nuts, and other processing methods.
1.2 Bending Lower Die
The bending machine's lower die includes bending lower dies, deep insertion lower dies, flattening lower dies, etc.
1.2.1 Bending Lower Die
The selection of the bending lower die is primarily based on the thickness of the processed product. Currently, the standard for selecting the lower die at Yixin Company is 6T. Unless there are special circumstances, this standard is used for on-site operations. When large V-groove or small V-groove processing is required due to processing limitations, the bending coefficient needs to be adjusted accordingly.
Die Analysis: The diagram shows one type of bending lower die. The V-groove types mainly include 4V, 6V, 7V, 8V, 10V, 12, 16V, 25V, and some special large V-groove bending tools. The height of this bending lower die can be categorized into two types: 46 high and 26 high.
1.2.2 Deep Insertion Lower Die
Die Analysis: The diagram shows one type of deep insertion lower die. The V-groove types mainly include 4V, 6V, 8V, 12, and some special deep insertion lower dies. It is suitable for bending angles between 30 and 180 degrees and deep insertion applications.
1.2.3 Flattening Lower Die
Currently, the company does not have a dedicated flattening lower die. In general, a regular bending die is used as a substitute.
2. Forming Methods of Bending Machine
2.1 L-Bending
L-bending is the basic bending shape, with bending angles ranging from 30 to 180 degrees.
For sharp bending angles, deep insertion lower dies and sharp upper dies are selected. For bending at 90 degrees or obtuse angles, any type of die can be selected for processing.
2.1.1 Locating Principles for L-Bending
A: The principle is to use two rear fixed stops (two points) and align them with the workpiece shape.
B: When using a single rear fixed stop, pay attention to the deviation and ensure it aligns with the bending dimension on the same centerline.
C: For small bends, backstop processing is preferred.
D: It is better to position the rear fixed stop slightly lower in the middle (to prevent the rear fixed stop from lifting during positioning).
E: It is better to position the edge closer to the rear fixed stop.
F: Long edge positioning is preferred.
G: Auxiliary positioning can be done using fixtures (for diagonal or irregular edge bending).
2.1.2 Considerations for Internal L-Bending
A: When bending with the mold in the correct position, the rear fixed stop needs to be pulled back to prevent deformation of the workpiece during bending.
B: When performing internal bending on large workpieces, the large outer shape and small bending area make it difficult for the tooling and bending area to overlap, leading to difficulties in workpiece positioning or damage.
2.1.3 Considerations for External L-Bending
A: When bending small dimensions, check for interference between the upper die and the rear fixed stop.
B: When the hole distance is close to the bending line or the bending edge dimension is smaller than half of the V-groove, pay attention to the material stretching during bending.
2.1.4 Special Bending Methods for L-Bending
A: Eccentric Bending Method
Process Analysis:
Eccentric bending has differences in the installation direction of the lower die. The distinction is made based on whether the material stretching occurs on the inner side or outer side of the bending line. Additionally, eccentric bending is a special processing method that carries certain risks and should not be used unless necessary.
B: Bending After Line Pressing Method
Process Analysis:
Due to the shearing effect of eccentric bending, it is not suitable for products with high surface requirements. The timing for using the line pressing bending method is the same as eccentric bending. Before bending, an 88-degree tool or a dedicated line pressing die can be used to press a line at the bending line, and then the bending is performed using a regular die.
C. Small V-Bending with Large Angle and V-Groove Pressing
Process Analysis: First, use a small V-groove to bend to a large angle, and then use a regular die for bending. This processing method avoids the issue of the unfolded dimension being too small when directly bending with a small V-groove.
D. Bending with Shims
Process Analysis: This method is mostly suitable for products with strict requirements for external shape. However, considering the cost, it is generally limited to sample processing.
The above four processing methods can also be combined for better forming results.
2.2 Z-Bending
Definition: Z-bending refers to the bending process where one bend is in the opposite direction of the other.
The processing range for standard bending: The height of Z-bending should be greater than the center distance of the V-groove plus T.
The minimum size for processing is limited by the mold used, while the maximum size is determined by the size of the bending machine.
2.2.1 Steps for Z-Bending
A: First, use the L-bending method to create an L-bend.
B: Use the L-bend positioning method to create the Z-bend.
(Alternatively, use the other side of the L-bend to create the Z-bend.)
2.2.2 Locating Principles for Z-Bending
A: The premise for positioning is convenience and good stability.
B: Generally, the positioning is the same as in L-bending.
C: When performing secondary positioning, the workpiece should be flush with the lower die.
2.2.3 Considerations for Z-Bending
A: The bending angle in L-bending must be accurate, generally requiring around 89.5 to 90 degrees.
B: The rear fixed stop should be set to pull back to prevent workpiece deformation.
2.2.4 General Methods for Z-Bending
A: Consider the processing sequence shown in the diagram, first bend 1 and then bend 2.
B: Another method is to first create the L-bend and then perform the Z-bend, ensuring that the Z-bend does not interfere with the machine.
a: If there is interference, bend 1 to a large angle, then bend 2, and finally apply pressure to 1.
b: If there is no interference, follow the general method for Z-bending, first bend 1 and then bend 2.
C: For two acute angle Z-bends, first bend to 90 degrees, then insert 2, and finally insert 1.
2.2.5 Special Methods for Z-Bending:
A: Eccentric lower die processing.
B: Bending with a small V-groove.
C: First bend to a large angle and then apply pressure.
D: Use a ground lower die.
2.2.6 Other Methods for Z-Bending:
A: Bending with step difference dies.
B: Forming with an easy mold.
2.3 N-Bending
Definition: N-bending refers to the process of bending twice continuously on the same processing surface.
2.3.1 General Considerations for N-Bending:
A: The angle of the first bend should be less than or equal to 90 degrees.
B: When performing the second bend, the rear fixed stop should be based on the processing surface.
2.3.2 Special Methods for N-Bending:
A. When there is slight interference between the Y dimension of N-bending and the upper die ==> Bend N times and then use a flattening die for shaping.
B. When there is significant interference between the Y dimension of N-bending and the upper die:
==> Bend A to the interference point after line pressing, then use C positioning to bend B, and finally use a combination of flattening die and shims for shaping.
C: Use a grinding tool for processing.
2.4 Arc Bending
Arc bending can be divided into two methods: bending with bending dies and bending with arc tools. Arc tools can be further classified into fixed type and round bar type.
2.4.1 Considerations for Processing:
A: When using a 90-degree lower die, there may be cases where the bending is not in place. Therefore, manual pushing or, if conditions permit, using an 88-degree lower die is needed.
B: It is advisable to use inspection fixtures to ensure the dimensional accuracy of the workpiece.
C: When bending a 90-degree arc, the lower die selection is 2(R+T).
3. Bending Process Arrangement
3.1 Basic Principles of Bending Process Arrangement
A: Bend from the inside to the outside.
B: Bend from small to large.
C: Bend general shapes first, then bend complex shapes.
D: The bending in previous processes should not affect the subsequent processes.
3.2 Examples of Process Arrangement
No matter how complex the workpiece is, it can be broken down into several types of processing methods. Therefore, it is necessary to master the operation methods of each bending method and learn to integrate and apply them in order to rationally arrange the bending process for different workpiece shapes.
4. Selection of Positioning Reference
A: Position based on the nearest edge.
B: Position based on the wider edge.
C: Preferably position based on the un-bent or minimally bent edge to reduce cumulative errors.
D: For sheet metal parts, position based on burr-free and contact edges.
E: Position based on the edge with minimal workpiece deformation.
F: Preferably select two rear fixed stops for positioning.
G: Auxiliary positioning can be added at both ends of the die, such as magnets.
H: For irregular workpieces, use LASER cutting fixtures for positioning.
I: Avoid positioning for large angle or U-shaped bending.
5. Principles for Selecting Bending Machines for On-site Operations
A: Select the machine based on the bending width.
B: Select the machine based on the bending length.
C: Select the machine based on the required bending pressure.
D: Select the machine based on the number of processing stations.
E: Select the machine based on the type and quantity of machines on-site.
F: Select the machine based on specific mold requirements.
G: Select the machine based on avoidance requirements.
H: Select the machine based on the range of movement of the rear fixed stop.
I: Select the machine based on the shape of the rear fixed stop.
6. Methods for Controlling Bending Dimensions
A: Avoid cumulative errors by measuring the unfolded dimension after each bend.
B: Avoid relying on already bent edges for positioning and avoid large angle positioning.
C: For products that require positioning based on already bent edges, the angle of the previous bend should be slightly less than 90 degrees.
D: Ensure the accuracy of measuring tools before processing.
E: Conduct initial inspections before formal processing and perform regular inspections during the process.
F: Select a suitable machine based on the precision requirements of the processed product.
G: Avoid using tools with different centers and ensure that the upper die tips are in line before processing.
H: Choose appropriate processing methods and process arrangement techniques to simplify the difficulty of processing.
I: Ensure accurate positioning and promptly inspect any positioning abnormalities.
